California Sea Otters Mysteriously Declining Despite Protection

The world’s cutest furry sea creature, the California sea otter, has been making a slow recovery since it was nearly wiped off the map by 150 years of hunting for it’s ultra-soft, waterproof fur. But despite being federally protected, the creature’s numbers are going down again, and no one is sure why.

Annual surveys of the California sea otter population, which are averaged over three years to compensate for variability in observation conditions, show the overall population has declined by nearly 4 percent compared to estimates in 2009, and the number of sea otter pups has declined by 11 percent. The otter’s range along the central California coastline has also shrunk by nearly 30 miles.

“Right now we don’t know the specific causes of the decline,” said biologist Tim Tinker of the U.S. Geological Survey, lead scientist of the annual otter survey. “All our data point to a combination of factors, both natural and human caused.”

The sea otters have been getting thinner and smaller relative to otters of the same age and sex in past years, says Tinker, which means they are having a harder time finding food. The number of shark attacks has also gone up, as have the number of bacterial and viral infections found in the otters.

“Diseases that come from terrestrial sources are one of the factors that are also contributing to increased mortality,” Tinker added.

Sea otter population numbers from 1985-2010

One of those diseases is Toxoplasma gondii, which is spread to otters when the fecal matter of infected cats gets washed out to sea, says Tinker, but there are other diseases as well.

To understand how to most effectively help the otters recover, Tinker says they plan to compare different sea otter populations along the California coast and populations of the northern sea otter, which lives on the coast from Alaska to Washington. By measuring the factors that could be leading to the sea otter decline in these various regions and comparing that to the relative health of their otter populations, scientists can analyze the relative impact of the different factors.

“Sea otters are a really good indication in the health of the coastal ocean,” said Tinker. “And what they’re telling us right now is that it’s not doing so well.“